14) A) Pathogens 15) A) Immune System 16) <span>C) Mouth, Esophagus, Stomach, Small Intestine, Large Intestine, Anus 17) A) Digestive 18) D) Esophagus 19) A) Circulatory system 20) D) Respiratory & circulatory
The hormone described above is the hormone Melatonin. Melatonin is a hormone secreted by the pineal gland in the brain, which helps regulate other hormones and maintains the body's circadian rhythm. This rhythm is an internal 24 hour clock that plays a critical role when we fall asleep and when awake. When it is dark the body releases more melatonin.
